WASHINGTON, D.C. — Bernie Sanders has taken on Wall Street, big oil producers, credit card issuers and private prison operators. Now the Democratic presidential candidate is taking aim at mergers among the nation’s biggest media companies.

In a Monday op-ed in the Columbia Journalism Review, the Vermont senator said that if elected president he would impose an “immediate moratorium” on approval of deals that would make media giants even bigger. “We are not going to rubber stamp proposals like the new plan to merge CBS and Viacom into a $30 billion colossus,” he wrote.

He also said that major media companies should be required to disclose whether their planned mergers could bring newsroom job cuts, and employees should be able to purchase media outlets through stock-ownership plans.

Sanders said he would appoint “new, progressive leadership” at the Federal Communications Commission to establish tougher media ownership rules that prevent extensive cross-ownership of newspapers and TV and radio stations.

“We will reinstate and strengthen media ownership rules, and we will limit the number of stations that large broadcasting corporations can own in each market and nationwide,” he added. “We will also direct federal agencies to study the impact of consolidation in print, television and digital media to determine whether further antitrust action is necessary.”

Sanders reiterated his pledge to appoint an attorney general and federal trade commissioners who would take a tougher stance on antitrust enforcement against tech powerhouses such as Facebook Inc. and Alphabet Inc.’s Google.

“More than two centuries after the Constitution was signed, we cannot sit by and allow corporations, billionaires and demagogues to destroy the Fourth Estate, nor can we allow them to replace serious reporting with infotainment and propaganda,” Sanders wrote.